Deep rolling tool for blade fatigue life enhancement

ABSTRACT

A device and methods are provided for deep rolling. In one embodiment, a deep rolling tool for applying compressive stress with rolling elements includes a fork having a base section and a plurality of fork arms, each fork arm extends outwardly from the base section and the fork arms are separated from one another to form an opening. The deep rolling tool may also include rolling elements, wherein each rolling element is mounted at the distal end of a fork arm, and the rolling elements are configured to apply a compressive stress to articles received by the deep rolling tool.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/567,522, now U.S. Pat. No. 9,573,175, filed on Dec. 11, 2014, whichclaims priority to U.S. Provisional Application No. 61/917,496 filed onDec. 18, 2013 and titled Deep Rolling Tool for Blade Fatigue LifeEnhancement, the entire contents of each of these applications arehereby incorporated by reference in their entirety.

This application is also a continuation of U.S. patent application Ser.No. 14/567,575, now U.S. Pat. No. 9,567,575, filed on Dec. 11, 2014,which claims priority to U.S. Provisional Application No. 61/917,579filed on Dec. 18, 2013 and titled Deep Rolling Tool for Processing BladeRoot, the entire contents of each of these applications are herebyincorporated by reference in their entirety.

FIELD

The present disclosure relates generally to machinery, and moreparticularly to deep rolling tools and methods for enhancing fatiguelife.

BACKGROUND

Peening, burnishing, and deep rolling are techniques that are used toinduce stress at the surface of a component. Conventional methods mayemploy some form of caliper to simultaneously pinch opposing sides of acomponent. These tools, typically referred to as ball point tools, oftenuse a caliper with ball bearings to pinch the component. FIG. 1illustrates a graphical representation of a conventional hydraulic tool100 which uses a pressurized hydraulic fluid to provide a clampingforce. Hydraulic tool 100 is a rigid body tool including hydraulicclamping elements 105 and 110 which are hydraulically actuated.Hydraulic tool 100 is supplied with a pressurized fluid by hydraulicinput valve 115. The main problem with hydraulic tools is that they arebulky which makes it difficult to process components. In addition, theuse of hydraulic ball bearing clamping elements 105 and 110 have a smallcontact zone which requires a lot of passes in order to process asurface, and thus, conventional hydraulic tools are slow. Further, thesetools require a high pressure pump which adds to complexity and cost.

A drawback of conventional machining operations ofpeening/burnishing/deep rolling is that they are typically slow andexpensive to perform. Another drawback is that conventional tools arenon-adjustable and may not be usable with certain componentgeometries/thicknesses.

Thus, there is a need for a machine and tool for applying stress toobjects.

BRIEF SUMMARY OF THE EMBODIMENTS

Disclosed and claimed herein are a device and methods for deep rolling.In one embodiment, a deep rolling tool for applying compressive stresswith rolling elements includes a fork having a base section and aplurality of fork arms, wherein each fork arm extends outwardly from thebase section and wherein the fork arms are separated from one another toform an opening, and a plurality of rolling elements, wherein eachrolling element is mounted at the distal end of a fork arm, and whereinthe rolling elements are configured to apply a compressive stress toarticles received by the deep rolling tool.

Other aspects, features, and techniques will be apparent to one skilledin the relevant art in view of the following detailed description of theembodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present disclosure willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 depicts a conventional hydraulic tool;

FIGS. 2A-2B depict a deep rolling tool according to one or moreembodiments;

FIG. 2C depicts a deep rolling tool and tool holder according to one ormore embodiments;

FIG. 3 depicts a rolling element according to one or more embodiments;

FIG. 4 depicts a graphical representation of deep rolling on a componentaccording to one or more embodiments;

FIG. 5 depicts a deep rolling tool according to one or more embodiments;

FIG. 6 depicts a machine including a deep rolling tool according to oneor more embodiments;

FIG. 7 depicts a process for a deep rolling tool according to one ormore embodiments;

FIG. 8 depicts a elements of a deep rolling tool according to one ormore embodiments; and

FIG. 9 depicts a graphical representation of bushing spacing accordingto one or more embodiments.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Overview and Terminology

One aspect of the disclosure relates to a device and methods for deeprolling to improve fatigue life in objects. According to one embodiment,a deep rolling tool is provided including crowned rollers to provide alocalized zone of compressive stress at the surface of a component.According to another embodiment, the deep rolling tool may be configuredto provide compressive stress to bladed elements, such as a turbineblade, compressor blade, fan blade, bladed disk, object with multipleblades, etc.

According to another embodiment, a machining device is providedincluding a deep rolling tool. The machining device may be a millingmachine or other device for processing bladed elements, such as turbineblades, compressor blades, fan blades, etc. According to one embodiment,the machining device may be a 5 axis milling machine.

In another embodiment, a deep rolling tool is provided with rollershaving eccentric bushings to allow for increased compressive stress. Theeccentric bushings can allow for alteration of shaft center linespacing.

According to another aspect of the disclosure, processes for using adeep rolling tool are discussed below. In one embodiment, a deep rollingtool may be positioned and applied to an article or component. The deeprolling tool may be repositioned and applied to another portions of anarticle, or to another article. For example, the deep rolling tool maybe applied to a bladed element, such as a particular blade of the bladedelement, and then repositioned to another blade of the bladed element.

As used herein, the terms “a” or “an” shall mean one or more than one.The term “plurality” shall mean two or more than two. The term “another”is defined as a second or more. The terms “including” and/or “having”are open ended (e.g., comprising). The term “or” as used herein is to beinterpreted as inclusive or meaning any one or any combination.Therefore, “A, B or C” means “any of the following: A; B; C; A and B; Aand C; B and C; A, B and C”. An exception to this definition will occuronly when a combination of elements, functions, steps or acts are insome way inherently mutually exclusive.

Reference throughout this document to “one embodiment,” “certainembodiments,” “an embodiment,” or similar term means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment. Thus, the appearancesof such phrases in various places throughout this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner on one or more embodiments without limitation.

Exemplary Embodiments

Referring now to the figures, FIGS. 2A-2B depict a deep rolling toolaccording to one or more embodiments. Deep rolling tool 200 may beconfigured to apply compressive stress with rolling elements. As shownin FIG. 2A, deep rolling tool 200 includes a fork 205 with fork arms 210and 215. Fork arms 210 and 215 extend outwardly from base section 230and the fork arms are separated from one another to form opening 220.Fork 205 may be a flexible fork tool configured to provide a compressiveforce based on the flexural stiffness of the plurality of fork arms 210and 215. The force is applied by expanding fork arms 210 and 215. Theforce can be tailored to increase non-linearly with expansion. Accordingto one embodiment, deep rolling tool 200 includes a plurality of rollingelements, 225 a-225 b mounted at the distal end 235 of a fork arm.Rolling elements 225 a-225 b are configured to apply a compressivestress to articles received by the deep rolling tool.

According to one embodiment, fork arms 210 and 215 of deep rolling tool200 are flexible, and therefore lack any pivot. When deep rolling abladed element, the configuration of deep rolling tool 200 is notconstrained by the depth from the blade edges to which compressiveresidual stresses are imparted, and is not constrained by the bladespacing. In addition, material of the bladed element is pushed to thecenter of the blade by deep rolling tool 200 to form continuous zones ofcompressive residual stress along the edges of rolling elements. Deeprolling tool 200 may have redundant degrees of freedom which can beadjusted for dimensional variations in new or repaired blades.

FIG. 2B depicts a frontal view of deep rolling tool 200 including forkarms 210 and 215. Rolling elements 225 a-225 b may be mounted to forkarms 210 and 215. According to one embodiment, each rolling elementincludes bushings, shown as 240 a-240 b for rolling element 225 a and241 a-241 b for rolling element 225 b.

According to one embodiment, deep rolling tool 200 does not require asocket to receive a burnishing element. Burnishing is a surface finishenhancement process, while deep rolling tool 200 provides sub-surfaceintegrity enhancement processing.

According to one embodiment, deep rolling tool 200 does not require anactuator, rather force control may be obtained by the non-linearstiffness of the fork arms 210 and 215 (e.g., stiffness with respect tothe deflection of the fork arms). Unlike control of a hydraulic element,deep rolling tool 200 may not require precise force control. Forexample, deep rolling tool 200 can apply a higher force to thickersections of an element due to the greater deflection of the fork arms.Fork arms 210 and 215 of deep rolling tool 200 may be configured toprovide a depth of subsurface deformation and percentage of cold workbased on two-dimensional prototyping of objects to be rolled.

Deep rolling tool 200 can avoid damage to neighboring regions of asingle blade or adjacent blade since rollers and fork arms may enter theblades in a chord-wise direction. Deep rolling tool 200 may becharacterized as having an unbiased tool path configuration to ensurethat peening forces do not exert a local twisting moment to bladesurfaces.

According to one embodiment, rolling elements 225 a-225 b are eachcrowned rollers to provide a compressive force based at least on theflexural stiffness of fork arms 210 and 215.

Referring now to FIG. 2C, a deep rolling tool and tool holder aredepicted according to one or more embodiments. Deep rolling tool 200 isdepicted in FIG. 2C mounted to tool holder block 250. In certainembodiments, tool holder block 250 may hold deep rolling tool 200 in afixed position. In other embodiments, tool holder block 250 may beconfigured to position deep rolling tool 200. Tool holder block 250 maybe configured to rotate fork 205 via rotary spine 255 in certainembodiments. Rotary spine 255 may allow for rotation of the deep rollingtool during repositioning, and in some cases during deep rolling.

According to one embodiment, deep rolling tool 200 is configured toapply residual stress to at least one of a turbine blade, compressorblade, fan blade, bladed disk, bladed element and metal object ingeneral. The compressive stress can improves fatigue life of thearticle, such as a bladed object. Rolling elements 225 a-225 b apply aresidual stress which inhibits crack propagation in an article.

In one embodiment, deep rolling tool 200 may be configured to apply acompressive stress to improve at least one of fatigue life of thearticle, surface finish of the article and aerodynamic performance(e.g., improved compressor efficiency) of the article. With respect tosurface finish, the compressive stress and/or rolling by deep rollingtool 200 may improve received articles to allow for a surface finishthat is suitable for airfoil applications and combustion enginecomponents such as turbine blades, compressor blades, fan blades, etc.In certain embodiments, deep rolling tool 200 may improve surface finishto allow for a roughness average of 0.5 μm to 10 μm. By improving thesurface finish, deep rolling tool 200 may heal surface defects, whichalso can improve fatigue performance.

FIG. 3 depicts a rolling element according to one or more embodiments.According to one embodiment, crowned roller 300 includes minor radius310 for contacting articles received by the rolling tool, and a majordiameter 305 for providing a load capacity. Crowned roller 300 includesa hollow center portion 315 for coupling to a bushing, and shaft forcoupling to a fork arm.

In one embodiment, each rolling element, such as crowned roller 300, issecured to a fork arm with roller bushings. Each rolling elementincludes a center axis and rotates about its center axis, and whereinthe center axis of a rolling element is parallel to the central axis ofanother rolling element. According to another embodiment, a minimum gapmay be provided in between rollers to allow for fork arms to expand. Thegap spacing may be based on tip clearance of a bladed element andcrowned roller 300 may by sized to allow for rolling of bladed elementtips and converging sections.

FIG. 4 depicts a graphical representation of deep rolling on a componentaccording to one or more embodiments. Deep rolling tool 400 (e.g., deeprolling tool 200) is shown rolling with fork 405 and blade 410. A deeprolling tool according to one or more embodiments is designed tofunction similarly to commercial hydraulic tools but with simpler, morecompact operation and to produce a larger contact zone, thus reducingprocessing time. According to one embodiment, by using crowned rollersas opposed to ball bearings, it is readily possible to tailor the sizeof the contact zone by adjusting the minor (crown) radius and includinga flat of desired width. The major (roller) diameter can be madesufficiently large to enable the use of a compact roller bearing thathas sufficient load carrying capacity negating the need for a hydraulicsystem. According to preliminary fatigue testing, greater than 10.times.improvement in fatigue life may be achieved, as will be discussed withreference to FIG. 5 below.

According to one embodiment, deep rolling tool 400 may be configured topeen blade edges in the chord-wise direction, and peen blade tips.Rollers of deep rolling tool 400 may require a threshold gap before theyopen and exert opposing forces. In certain embodiments, the thresholdgap can be altered allow for the tool to enter the blade tip in aspan-wise direction.

In FIG. 4, bladed element 410 is mounted to machine 415. When deeprolling tool 400 is pressed on to the edge of blade 410, the fork armsof deep rolling tool 400 are forced apart which produces a reactionforce that is proportional to the amount of deflection. The roller andfork geometry are configured to provide a sufficiently large contactstress to locally yield the blade material generating a residualcompressive stress field. According to one embodiment, the residualstress generated by deep rolling tool 400 inhibits crack propagationfrom the blade edge

FIG. 5 depicts a deep rolling tool according to one or more embodiments.According to one embodiment, a deep rolling tool may be positioned by amachine including a positioning element. In FIG. 5, deep rolling tool505 is mounted to tool holder base 510 and positioning element 520.Positioning element 520 may be coupled to a machine, such as a millingmachines to position deep rolling tool as shown be the referencedirections and to rotate the tool as shown by the reference arrows inFIG. 5. By way of example, deep rolling tool 500 may be rotated aboutthe x axis in FIG. 5 based on rotary coupling 515. Positioning element520 may be configured for rotation about the z-axis as shown in FIG. 6.Deep rolling tool 500 may be incorporated into a machine, such as a 5axis milling machine in certain embodiments.

According to one embodiment, a machine, such as a milling machineincludes deep rolling tool 500 having a plurality of rolling elements,wherein each rolling element is mounted at the distal end of a fork arm,the rolling elements are configured to apply a compressive stress toarticles received by the deep rolling tool, and a positioning elementcoupled to the deep rolling tool, wherein the positioning element isconfigured to position the deep rolling tool and apply the deep rollingtool to an article. In certain embodiments, the machine is a 5-axismachine and the positioning element is configured to position the deeprolling tool in three dimensions, and rotate the tool in two dimensions.In one embodiment, a block of the deep rolling tool is mounted to thepositioning element, and a fork is perpendicular to the positioningelement. The deep rolling tool may be rotated along a central axis ofthe rolling tool by the positioning element. The positioning element maybe configured to move the rolling tool in an alternating motion from aretracted position to an extended position, such as a linear path. Deeprolling tool 500 may be configured to apply residual stress to at leastone of a turbine blade, compressor blade, fan blade, bladed disk, bladedelement and metal object in general.

According to another embodiment, a machine, such as a milling machineincludes deep rolling tool 500 having a plurality of rolling elementsand a positioning element coupled to the deep rolling tool, wherein thepositioning element is configured to position and apply the deep rollingtool to a bladed element. The positioning element of the machine may beconfigured to move the rolling tool in an alternating motion from aretracted position to an extended position, and/or in a linear path.

FIG. 6 depicts a machine including a deep rolling tool according to oneor more embodiments. As shown in FIG. 6, machine 600 is configured toposition tool holder 605 (which includes a deep rolling tool describedherein) and positioning element 610. Machine 600 may be configured toposition a deep rolling tool for a bladed element, shown as 615 in FIG.6. Bladed elements may be individual or coupled to a support, such as620, according to one or more embodiments. Machine 600 may be configuredto position and operate tool 605 based on one or more of atwo-dimensional model and three-dimensional model of an element, such asa bladed element or collection of bladed elements.

According to one embodiment, machine 600 and/or tool holder 605 mayinclude one or more elements to balance degrees of freedom. By way ofexample, the block of tool holder 605 may have an additional degree offreedom to rotate against a spring element (e.g., spring element). Thespring element and a thrust bearing within tool holder 605 may allow forthe deep rolling tool to rotate and return to a home position. Incertain embodiments, machine 600 and/or tool holder 605 may include oneor more elements restrain motion of a deep rolling tool duringoperation. As shown in FIG. 6, tool holder 605 includes y-notch 625. Inaddition, flange 630 which holds plunger 635 configured to engagey-notch 625. In a home position, plunger 635 rests in the center notchof y-notch 625. During operation, rotation stress on the tool and toolholder 605 may be counteracted by plunger 635 as the plunger contactsraised portions of y-notch 625. Plunger 635 may provide a restrainingmoment (e.g., force) to tool holder 605.

According to one embodiment, machine 600 may be a 5 axis milling machineto enable in-situ processing of bladed elements (e.g., integrated bladedrotors). As shown in FIG. 6, the fork of a deep rolling tool is mountedin a block that allows rotation about the machines spindle axis andabout the fork's axis that is at 90 degrees to the spindle axis. Thesetwo additional degrees of freedom enable the tool to process a bladewith complex curvature without imparting any significant bending loadson the blade. The bearings in the tool holder block on the spindle axisenable the milling machine to be run with its spindle rotating withoutthe deep rolling tool spinning This is done as machines often requirethe spindle to be turning in order to run a program and it also muchless likely to cause any problems to the spindle bearings. The tool mayinclude spring loaded centering mechanisms on both of the tool holder'saxes so that the tool will return to its home position when not in usebut will not induce any significant forces on the blade. According toone embodiment, simplicity and compactness, and by extension, low costare the principle benefits vs. competing designs.

The deep rolling tool of one or more embodiments described herein can bereadily adapted for use with standard tool holders. For example, such atool is compact to allow for fit in between neighboring blades whileprocessing a blade near its root. In one embodiment, a machine 600 maybe a 5 axis milling machine that would typically be used for machiningan integrally blade rotor (IBR). The deep rolling tool may be simple,compact and capable of processing the leading and trailing edges ofIBRs, while still installed in the machine.

FIG. 7 depicts a process for a deep rolling tool according to one ormore embodiments. Process 700 may be initiated by positioning a rollingtool relative to a bladed element at block 705. For example, the deeprolling tool may be applied to a bladed element. At block 710, rollingmay be initiated or continued in some circumstances. A milling machinemay be configured to execute process 700 and may be configured todetermine when a position change for the deep rolling tool is required.When a position change is not required (e.g., “NO” path out of decisionblock 715), the milling machine continues to deep roll at block 710.When a position change is required (e.g., “YES” path out of decisionblock 715), the milling machine repositions the rolling tool at block710.

Process 700 may continue with the machine determined if rolling iscomplete a decision block 725. When rolling is not complete (e.g., “NO”path out of decision block 725), the milling machine continues to deeproll at block 710. When rolling is complete (e.g., “YES” path out ofdecision block 725), the milling machine removes the rolling tool atblock 735.

Referring now to FIG. 8, elements of a deep rolling tool are depictedaccording to one or more embodiments. According to one embodiment,rolling elements 800 of a deep rolling tool include eccentric rollerbushings. FIG. 8 depicts a pair of roller elements 800 wherein eachrolling elements includes a crowned roller, shown as 810 and 815, andeach rolling element includes bushings, shown as 805 a-b and 816 a-b.According to one embodiment, bushings 805 a-b and 816 a-b may beconfigured to alter the center line spacing of the rolling elements. Inaddition, the compressive force applied by a deep rolling tool may beincreased based on the position of eccentric bushings, such that a forkof a deep rolling tool provides a compressive force based, at least inpart, on the flexural stiffness of the plurality of fork arms and theposition of the eccentric roller bushings.

FIG. 9 depicts a graphical representation of bushing spacing accordingto one or more embodiments. According to one embodiment, rollingelements 900 of a deep rolling tool may include eccentric bushings suchthat rotation of the bushing element adjusts shaft center line spacing.FIG. 9 depicts the shaft center line spacing at two positions where themaximum and minimum contact stress are applied. The addition ofeccentric bushings between the fork and the roller shafts of the deeprolling tool enables the distance between the shaft center lines to beadjusted.

Position 905, for bushings 910 and 911 of rolling elements 915 and 916,relates to a first position, wherein the rolling elements 915 and 916provide less contract stress. Position 950, for bushings 915 and 916 ofrolling elements 910 and 911, relates to a second position, wherein therolling elements 910 and 911.

According to one embodiment, a deep rolling tool includesinterchangeable rollers having varying geometries that affect thecontact stress when processing a part. While having a fixed flexuralstiffness fork with various roller geometries may be applicable to arange of typical blades, the ability to adjust the applied force willbroaden its range.

According to one embodiment, bushings 910 and 911 may each be set with amirror position relative to one-another. With this modification therollers can be adjusted so that there is a gap between them at one endof the adjustment range through to being pre-loaded at the other end ofthe range. While this configuration doesn't alter the stiffness of thefork arm, it does affect the applied pinch force. In certainembodiments, the configuration does not cause the rollers to runeccentrically on their shafts, rather the shaft center line spacing isaltered. Reference marks on the bushing flanges can simplify the processof setting them to be in mirror positions, which may be a requirement tokeeping the shafts parallel. Other embodiments may include adding areinforcing strap around the fork arms such that changing its positionalong the arms it effectively alters the arm length and hence thestiffness.

In another embodiment, the deep rolling tool may include a screwadjustment to alter the roller spacing by forcing the arms apart ortogether which has a similar effect to the eccentric bushing concept. Incertain embodiments, the benefit of eccentric bushings can provide agreater range of adjustment for a deep rolling tool, thus allow for agreater range of blade geometries. While it may not be possible to havea single tool suitable for all blade shapes, it will reduce the numberof tools required.

While this disclosure has been particularly shown and described withreferences to exemplary embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the claimedembodiments.

What is claimed is:
 1. A deep rolling tool for applying compressivestress, the deep rolling tool comprising: a first fork arm and a secondfork arm each integrally formed with and extending outwardly from a basesection, wherein the first fork arm and the second fork arm areseparated from one another to form an opening; a first rolling elementrotatably secured to a distal end of the first fork arm; a secondrolling element rotatably secured to a distal end of the second forkarm; wherein the first fork arm and the second fork arm are configuredto locate the first rolling element and the second rolling element in afacing spaced relationship with respect to each other; and wherein thefirst rolling element and the second rolling element apply a compressivestress to an article received in the opening, wherein the first rollingelement and the second rolling element each have a crowned roller, thecrowned roller having a minor radius for contacting the article receivedby the rolling tool, and a major diameter adapted to provide a loadcapacity, and wherein the applied compressive stress of the firstrolling element and the second rolling element is dependent upon aflexural stiffness of the first fork arm and the second fork arm.
 2. Thedeep rolling tool of claim 1, wherein the deep rolling tool isconfigured to apply residual stress to the article and the article is atleast one of a turbine blade, a compressor blade, a fan blade, a bladeddisk, a bladed element and a metal object.
 3. The deep rolling tool ofclaim 1, wherein the compressive stress improves at least one of afatigue life of the article, a surface finish of the article and anaerodynamic performance of the article.
 4. The deep rolling tool ofclaim 1, wherein the first rolling element and the second rollingelement apply a residual stress that inhibits crack propagation in thearticle.
 5. The deep rolling tool of claim 1, wherein the first rollingelement and the second rolling element are secured to the deep rollingtool with roller bushings.
 6. The deep rolling tool of claim 1, whereinthe first rolling element and the second rolling element each rotateabout a center axis and wherein the center axis of the first rollingelement is parallel to the center axis of the second rolling element. 7.The deep rolling tool of claim 1, wherein the article is a bladedobject.
 8. The deep rolling tool of claim 1, wherein first rollingelement and the second rolling element are interchangeable rollershaving varying geometries that affect the compressive stress applied tothe article received in the opening.
 9. The deep rolling tool of claim1, wherein first rolling element and the second rolling element includeeccentric bushings.
 10. A deep rolling tool for applying compressivestress with rolling elements, the deep rolling tool comprising: a firstfork arm and a second fork arm each integrally formed with and extendingoutwardly from a base section wherein the first fork arm and the secondfork arm are separated from one another to form an opening; a firstcrowned rolling element rotatably secured to a distal end of the firstfork arm; a second crowned rolling element rotatably secured to a distalend of the second fork arm; wherein the first fork arm and the secondfork arm locate the first crowned rolling element and the second crownedrolling element in a facing spaced relationship with respect to eachother and wherein the first fork arm and the second fork arm extendoutwardly from the base section; and wherein the first crowned rollingelement and the second crown rolling element apply a compressive stressto an article located between the first crowned rolling element and thesecond crowned rolling element, wherein the applied compressive stressis dependent upon a flexural stiffness of the first fork arm and thesecond fork arm.
 11. The deep rolling tool of claim 10, wherein thefirst crowned rolling element and the second crowned rolling elementeach have a major diameter adapted to provide a load capacity.
 12. Thedeep rolling tool of claim 10, wherein the deep rolling tool isconfigured to apply residual stress to the article and the article is atleast one of a turbine blade, a compressor blade, a fan blade, a bladeddisk, a bladed element and a metal object.
 13. The deep rolling tool ofclaim 10, wherein the compressive stress improves at least one of afatigue life of the article, a surface finish of the article and anaerodynamic performance of the article.
 14. The deep rolling tool ofclaim 10, wherein the first crowned rolling element and the secondcrowned rolling element are adapted to apply a residual stress thatinhibits crack propagation in the article.
 15. The deep rolling tool ofclaim 10, wherein the first crowned rolling element and the secondcrowned rolling element are secured to the deep rolling tool with rollerbushings.
 16. The deep rolling tool of claim 15, wherein the rollerbushings are eccentric bushings.
 17. The deep rolling tool of claim 10,wherein the first crowned rolling element and the second crowned rollingelement rotate about a center axis wherein the center axis of the firstcrowned rolling element is parallel to the center axis of the secondcrowned rolling element.
 18. The deep rolling tool of claim 10, whereinthe article is a bladed object.
 19. The deep rolling tool of claim 10,wherein first crowned rolling element and the second crowned rollingelement are interchangeable rollers having varying geometries thataffect the compressive stress applied to the article.
 20. The deeprolling tool of claim 10, wherein first crowned rolling element and thesecond crowned rolling element include eccentric bushings.